It will be understood that a Laser is an amplifier of light, and that the word laser is a coined word of the letters thereof, being "Light Amplification Stimulation of Electromagnetic Radiation."
The conventional manner of exciting CW ion lasers is to use electron collisions in the positive column region of a low pressure gas discharge.
A positive column has roughly a Maxwellian electron energy distribution with a mean electron energy of 3 to 8 electron volts (eV), depending upon pressure, current density, bore diameter and magnetic field strength. Such bore being, of a conventional laser instrument tube. However, ionization and excitation cross sections of many upper laser levels peak above 100 eV. Hence, only those energetic electrons in the tail of the Maxwell-Boltzman energy distribution are energetic enough to provide direct excitation. As a consequence, very large current densities (hundreds of A/cm.sup.2) are generally required to excite noble gas ion lasers, resulting in laser operating efficiencies of 5.times.10.sup.-4. In the case of metal vapor ion lasers, the metal impurity, when added to the discharge, drastically lowers the electron temperature of the positive column plasma. As a result, the metal vapor concentration and the electron temperature cannot be independently optimized. The electron energy characteristics of the positive column become even more undesirable for UV and VUV ion lasers where the upper laser levels are in multiply ionized species. The laser operating efficiencies for Ar.sup.++ and Kr.sup.++ lasers, for example, are typically 10.sup.-4. Hollow cathode ion lasers have an electron beam component in the electron distribution, but it is small and inefficiently produced and impractical as the beam component accounts for typically only 10% of the total discharge current.
Applicants have perfected electron beam plasmas of a high density of high energy electrons, created by their electron beams in a very sufficient way by their new d.c. electron guns use. Also, in this invention the parameters of the electron beam discharge are independently optimized from the density of metal vapor concentration when metal vapor is used as laser material.